linux-kernel - Re: [take13 1/3] kevent: Core files.

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Message-ID: <20060824200322.GA19533@infradead.org>
Date:	Thu, 24 Aug 2006 21:03:22 +0100
From:	Christoph Hellwig <hch@...radead.org>
To:	Evgeniy Polyakov <johnpol@....mipt.ru>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	Ulrich Drepper <drepper@...hat.com>,
	Andrew Morton <akpm@...l.org>, netdev <netdev@...r.kernel.org>,
	Zach Brown <zach.brown@...cle.com>,
	Christoph Hellwig <hch@...radead.org>
Subject: Re: [take13 1/3] kevent: Core files.

One question on the implementation of kevent_user_ctl_modify/
kevent_user_ctl_remove/kevent_user_ctl_add:  What benchmarks did you
do to add the separate 'fastpath' with the single onstack ukevent
structure if there are three or less events?  I can't believe this
actually helps in practice for various reasons:

 - you add quite a lot of icache footprint by duplicating all this code
 - kmalloc is really fast
 - two or three small copy_from/to_user calls are quite a bit slower
   than one that covers the size of all of them.
-
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